AbstractLeakage in underground water pipes has become critical because of increasing water demand. Many studies have been conducted based on the knowledge of soil–water interaction, but few of them have investigated the internal erosion and possible zones forming around cracks as a result of leakage. This experimental investigation set out to achieve a better understanding of the mentioned problem. An unplasticized PVC pipe with a longitudinal crack was installed in a box with different types of soil, then water was flowed through the pipe. The aim was to determine the geometry of the zones possibly forming around the crack. The observation was made possible by installing the pipe beside a glass wall situated on the front face. Two zones (fluidization and mobile bed) with different directions that were geometrically different with soil types and water head pressures were observed. The effects of soil properties [e.g., median diameter (D50), Atterberg limits, porosity, and hydraulic conductivity] were also determined, and their relationships with the height, width, and maximum cross-sectional area of the mentioned zones were studied. The results demonstrated that the maximum height and maximum area of the zones were strongly correlated with water pressure.Practical ApplicationsThe significance of water in all aspects of human life is undeniable. Nowadays, a huge amount of water is wasted due to various reasons such as water loss from damaged parts of water distribution systems. The amount of leaking water can be impacted by factors including the surrounding environment, which is soil for underground pipelines. In addition, research has shown occurrence of fluidization phenomenon in which water and soil mixture around the leakage position flow in a confined area. Every underground infrastructure, including the leaking pipe, situated in the fluidized area can be affected and damaged. Knowing the mechanism of fluidization and factors affecting this area can thus help prevent underground facilities from damage. This experimental investigation examined the effects of pressure on the shape and size of zones around the leakage position. Furthermore, changes in the geometry of the mentioned area were studied by different types of surrounding soil.